Immersion thermocouple construction



Mal'Ch 16, 1954 TINGLE ET AI.

IMMERSION THERMOCOUPLE CONSTRUCTION Filed Jan. 17, 1951 A TTOENEYS Patented Mar. 16, 1954 IMMERSION THERMOCOUPLE CONSTRUCTION Leroy Tingle, Canton, and James Middleton Brandon, Louisville, Ohio, assignors to Republic Steel Corporation, Cleveland, Ohio, a corporation of New Jersey Application January 17, 1951, Serial No. 206,478

(Cl. 13G- 4) 12 Claims.

The present invention relates generally to the art of measuring heat and temperature and is more particularly concerned with a novel immersion thermocouple for determining temperatures of molten metals of relatively high melting point temperature.

It has long been customary in the manufacture of immersion-type thermocouples, such as those used in the steel industry, to provide a casing of refractory material to protect metal parts of the assembly from contact with molten slag and metal and from direct exposure to furnace heat. This casing usually extends from the hot end or immersion end of a couple, which it partially covers, to a point near the opposite or cold end of the couple and encloses a large portion of the length of the couple structure. While this casing is satisfactory and effective as a heat insulating element, it has never been at all satisfactory from the standpoint of maintenance and repair costs, being subject in use to extremes of temperature and to physical impacts, which shortly result in spalling and breakage of the casing. Consequently, casings of this kind in commercial operations are normally useable only for about three or four temperature determinations before extensive patching or complete replacement of the casing body is required. As a result, a relatively large labor force is required for the sole purpose of keeping these couples in service and this labor is not a negligible factor in the costs of operation of a furnace.

Others have heretofore made serious efforts to overcome these difficulties While retaining the advantages inherent in these casings. However,

to the best of our knowledge, none of these efforts has resulted in any satisfactory solution to the problem. One would have the refractory casing so thick that it would have enough mechanical strength to withstand the abuse incident to its normal use. The resulting device, however, is so cumbersome and heavy that one man could not handle it and no economic advantage is gained.

According to anotherrproposal, a pipe would be provided to receive and enclose and protect that portion ofthe refractory body subject to hardest service. In practice, however, this was no better than the otherv proposal for if the pipe is relatively light and thin, it will not withstand the heat from the furnace well enough to extend apprecably the useful life of the couple assembly. 4On. theother hand, if' the pipe employed is; heavy enough to withstandzthe severe service conditions, the assembly is too heavy for one man to handle. Moreover, in one respect at least, this proposal is even less practical than the other one because heat is retained in theassembly by the pipe with the result` that'thetemperature in the assembly will go higher thanV 400 F. and platinum losses will becomeprohibitive.

In accordance with the present invention, all the advantages of the refractory material body will be retained undiminished and atr the same time, the shortcomings and difliculties of .the prior art can be entirely overcome and protection for refractory casings can be obtained. In fact, by virtue of this invention, the life of these refractory bodies may be increased on anraverage from 15 to 40 times over that of prior art devices. Furthermore, these novel results can be obtained in an economical manner and without requiring special skills or tools in addition to those heretofore involved in the Amanufacture and maintenance of immersion thermocouples. Still further, where this invention is employed, a relatively thin coat of good insulating material may be used without the temperature inside the assembly ever exceeding 400" F. so that platinum losses are maintained at a minimum. Moreover, assemblies of this. invention are not affected by the type .ofsiag or atmosphere to which they are subjected'and if by accident a portion of the arm or hot end of the assembly is dipped into a molten metalbath and a part of the outer reinforcing and'protecting metal shell is melted, the remaining portion of the shell, nevertheless, will remain in place and maintain the refractory casing in place and intact.

This invention is predicated upon our` surprising discovery that a Wire wrapped as va coil around a tube of refractory material, and thus itself defining an open ended tube, will not only not add noticeably to the weight of the thermocouple assembly, but will provide all the'protection for the refractory tube obtainable with metal pipes of such heavy construction thatthe resulting assemblies are impracticable. Furthermore, where the wire employed is baling wire or the like and is therefore, readily corroded under conditions of use, the metal shell takes on even greater protective characteristics and greater strength. This result is surprising in view of the fact as the metal of the coil deteriorates Coxidizes), its strength and its value as armor for thev refractory casing increases to a substantial degree. Apparently. coalescense of iron oxide particles formed on the coil f proceeds rapidly when the coil is subjected to furnacev heat and adjacent turns of the coil are thereby bound firmly and securely together in a thin and light but surprisingly strong construction.

Those skilled in the art will gain a further appreciation of the objects and advantages of this invention and will also gain a further understanding of the invention upon referring to the drawings accompanying and forming a part of this specification; in which:

Fig. 1 is a View partly in section of a thermocouple of this invention;

Fig. 2 is a side elevational View of four elements of the apparatus of Fig. l; and,

Fig. 3 is a View partly in section of another form of thermocouple of this invention.

Generally, the present invention contemplates insulating and protecting means for an immersion thermocouple assembly comprising a tubular body of refractory material to receive a portion of the assembly and a metal shell in the form of a wire coil gripping and encasing a portion of the tubular body to protect and reinforce the body and tc engage supporting structure for the assembly. Thus, an assembly embodying this invention generally comprises a conduit through which lead wires may extend, a tubular body of refractory material receiving and shielding a portion of the conduit from direct exposure to heat, and a metal shell comprising a coil of wire dening a tube gripping and encasing a portion of the tubular body.

|"ihe illustrated thermocouples comprise a pair of thermoelectrically dissimilar wires W attached to an electrical fitting F for engagement with a potentiometer, or other temperature indicating or recording device, and casing means for protecting the wires against fouling by molten baths in which they are immersed, or by the atmosphere, or the slag. A silica tube it having a closed lower end forms the immersion tip of the couple casing and receives the joined ends of wires W. The upper end of tube I is received in a hollow graphite plug il, which has tapered outer walls adapted to be received in a ared open end of a graphite sleeve I2. In the couple of Fig. l, an L-shaped metal pipe I4 having an externally threaded end portion adjacent to the other end of sleeve I2, extends to the other end of the couple, remote from tube I0. A relatively short section of pipe I5 having an externally threaded end portion is secured within sleeve I2 with said threaded portion extending therefrom to be engaged with an internally threaded coupling El whereby pipe I5 and the remaining parts of the immersion end of the casing are secured to the pipe I4.

Wires W are insulated from each other and other metal articles from fitting F to a point within sleeve i2 adjacent to tube I0, and their exposed portions are protected against contact with molten metal by cement which secures plug i to tube It and sleeve I2. Pipe I4, except for a short segment adjacent to fitting F is encased in a succession of layers of materials including a metal sleeve or tube 2l which extends about onethird of the length of the pipe. From the end of tube 2l to coupling Il the pipe is wound With asbestos rope 23 which is held in place by wire binding 2t and which also encases the coupling and abuts the adjacent end of sleeve I2. A refractory cement layer 25 encases all except the end portions of the assembly, extending from mid-way of the length of sleeve 2I to a point adjacent to the lower end of sleeve I2. The upper or handle portion of layer 25. which in use is normally engaged with door sill of a furnace, is wrapped and molded in asbestos tape 2S! and a baling or low carbon wire coil 33 which substantially covers the tape, adjacent turns of the coil being engaged to define a tubular body having open ends and substantially continuous side walls.

While we prefer that coil 30 be of baling wire, it may suitably be made of some other iron or steel wire, such as piano wire, or it may be made of non-ferrous metals and alloys including brass, copper, manganin, molybdenum, Monel, Nichrome, nickel and tungsten. The principal criterion for wire coil 30 is its ability to withstand furnace heat under conditions of normal use of the thermocouple assembly so that the refractory material casing will be protected for protracted periods of use against sharp temperature changes and physical shocks. Preferably, however, the wire employed should be of a composition that is not particularly resistant to oxidizing influences, unlike stainless steel wire for example, as otherwise secure bonding of the adjacent turns of the wire coil will not be realized and the resulting protecting metal shell, while generally satisfactory, may not produce every advantage set out above.

Coil 30 may be of any desired wall thickness and length but preferably is no heavier or longer than necessary to afford the desired protection for the refractory casing in ordinary use. We have found that normally, Wall thickness equal to the diameter of baling wire is adequate to assure the foregoing novel and important advantages of this invention. We have further found that extension of the coil to parts of the refractory casing, such as the portion of the casing covering the arm of the assembly and terminating adjacent to plug I I and tube I0, is not usually necessary. This hot end portion of the casing is not normally subject to impacts which might crack or break the casing and spalling due to drastic temperature changes is not severe in the regions where the casing overlies pipe Irl and serves as its primary protection against direct exposure to furnace heat.

The couple of Fig. 3 differs from that of Fig. l in that the casing is in two parts, viz. a handle or body 35 and a head 36 which is detachable from the body. Head 36 comprises a silica tube I6, a graphite plug II, and a graphite sleeve I2, which receives the joined or hot ends of the wires W, and forms the immersion end of the thermocouple. A straight metal tube 38 oncle-'ses the wire W and has an end portion received in and secured to sleeve I2, and an end portion 39 provided with external threads. A coupling Ill having internal threads is threadwise engaged with end 39 of the tube. Body 35 comprises a straight tube 4I having a threaded end portion 42 for engagement with coupling 4Q. Tubes 38 and 4I are both encased in asbestos rope 23, wire binding 24 and a refractory cement layer 25, as illustrated in Fig. 1. The cement layer, rope, and wire of heat 36 extend from the outer end of coupling 40 to sleeve I2. The cement layer covering tube 4I leaves end 42 exposed for engagement with coupling 40, and said layer is wrapped with asbestos tape 29, which is substantially completely covered by a wire coil 30 formed by tightly winding suitable wire around the tape after the manner illustrated in Fig. 1. y i

The cou'ple of Fig. 1 may be modified as illustrated in Fig. 3, that is, the elbow portionmay be made detachable from the straight body or handle portion of the couple. In this event-pipe I5 vwould extendv to a point beyond thev elbow, such as theV point to which coil 3B extends along said body toward said elbow. Pipe I4 would be correspondingly shortened but would be engaged with coupling Il and pipe I5 in the manner illustrated in Figs. 1 and 3, and both pipes would be covered as shown in Fig. 3. The pipe coverings would, of course, be separate and independent insofar as the two parts of the couple are concerned and at the point of engagement the cement layers, etc. would be formed to enable a tight joint to be made between the head or elbow portion and the handle of the couple.

In assembling the thermocouple of Fig. 1, wires W are threaded through pipe I d, coupling I1, pipe I5 and sleeve I2, and the exposed joined ends of the wires are inserted into silica tube I to .which plugrv Il has previously been cemented in fluid tight contact. Plug II is then pressed into tight contact with the lower end of the sleeve I2. Coupling Il is drawn up and the asbestos rope 23 and retaining wire 24 are Wound around pipe I4 and coupling Il. The assembly is then encased in cement layer 25 which is permitted to harden after tape 29 and wire coil 30 have been applied thereto.

Assembly of the couple of Fig. 3 may be made in generally the manner above described. When the head is to be placed, it may be disengaged from the body 25 by rotation of the head relative thereto followed by removal of wires W from within the head. The Wires are inserted in a new head which is then threadwise engaged with the body 35 by rotating the head relative to said body and engaging the new head with end l42 of the body.

In securing pipe I or pipe 38 to sleeve I2, a pin (not shown) is inserted through an opening in the upper side portion of the sleeve to engage a notch in the tube and thus retain the parts in relative position. A small clearance existing between the pipe and sleeve is then packed with cement which firmly joins the parts together upon hardening.

This is a continuation-in-part of our joint application, Serial No. 732,950, entitled Thermocouple Construction, filed March 7, 1947, which was converted into a sole application in the name of Leroy Tingle and on which U. S. Patent No.

2,556,238 was granted on June 12, 1951.

Having thus described the present invention so that those skilled in the art Will be able to gain a better understanding and practice the same, We

state that what we desire to secure by Letters i Paten is defined in what is claimed.

What is claimed is:

1. In an immersion thermocouple including a pair of thermoelectrically dissimilar wires and a casing of refractory material enclosing and protecting the wires, the combination of a hard, protecting and reinforcing metal shell gripping and encasing a portion of said casing for engagement with a supporting structure for the thermocouple, said metal shell comprising a coil of baling wire defining an open-ended tube.

2. In an immersion thermocouple including a pair of thermoelectrically dissimilar wires and a casing of refractory material enclosing and protesting the wires, said casing comprising a body portion to rest on a furnace door sill and a head or immersion end portion the combination of a hard, protecting and reinforcing metalv shell gripping and encasing the body portion of said casing for engagement with a supporting struc- ,6 ture for the thermocouple, vsaid metal shell comprising a coil of ferrous metal wire defining an enlongated tube open at each end and extending substantially to one end of the said casing.

3. In an immersion thermocouple including a pair of thermoelectrically dissimilar wires and a casing of refractory material enclosing and protecting the wires, said casing comprising a body portion to rest on a furnace door sill and a head or immersion end portion the combination of a hard, protecting and reinforcing metal shell gripping and encasing the body portion of said casing for engagement with a supporting structure for the thermocouple, said metal shell comprising a coil of ferrous metal wire defining an elongated open-ended tube having a substantially uniform wallY thickness approximating the diameter of said wire.

4. In an immersion thermocouple including a pair of thermoelectricaily dissimilar wires and a casing of refractory material enclosing and protecting the wires, said casing comprising a body portion to rest on a furnace door sill and a head or immersion end portion the combination of asbestos tape Wrapping on the outer surface of said casing and a hard, protecting and reinforcing metal shell gripping and encasing thev body portion of said casing and said wrapping for engagement with a supporting structure for the thermocouple, said metal shell comprising a coil of ferrous metal wire defining an open-ended tube.

5. Insulating and protecting means for an immersion thermocouple assembly comprising a tubular body of refractory material to receive a portionof said assembly, and a metal shell gripping and encasing a portion of said tubular body for protecting and reinforcing said body and for engagement with a thermocouple assembly supporting structure, said metal shell comprising a coil of baling wire defining an openended tube.

6. Insulating and protecting means for an immersion thermocouple assembly comprising a tubular casing of refractory material to receive a portion of said assembly, said casing comprising a body portion to rest on a furnace door sill and a head or immersion end portion and a metal shell gripping and encasing the body portion of said tubular casing for protecting and reinforcing said casing and for engagement with a thermocouple assembly supporting structure, said metal shell comprising a coil of wire defining an elongated tube open at each end and having a substantially uniform wall thickness approximating the diameter of said wire.

7. Insulating and protecting means for an immersion thermocouple assembly comprising a tubular casing of refractory material to receive a portion of said assembly, said casing comprising a body portion to rest on a furnace door sill and a head or immersion end portion asbestos tape wrapping covering a portion of the outer surface of said tubular casing, and, a metal shell gripping and encasing the body portion of said tubular casing and said Wrapping for protecting and reinforcing said casing and for engagement with a thermocouple assembly supporting structure, said metal shell comprising a coil of ferrous metal wire defining a tube open at its ends.

8. An immersion thermocouple assembly comprising an open-ended conduit through which lead wires of a thermocouple may extend, a tubular casing of refractory material receiving and shielding said conduit from direct exposure to Vfurnace heat, said casing comprising a body portion to rest on a furnace door sill and a head or immersion end portion and a metal shell gripping and encasing the body portion of said tubular casing for protecting and reinforcing said casing and for engagement with a thermocouple assembly supporting structure, said metal shell comprising a coil of wire defining an open-ended tube.

9. An immersion thermocouple for determining the temperature of molten metal comprising a pair of thermoelectrically dissimilar wires connected together at one end, and a covering for said Wires comprising a hollow graphite plug having a tapered upper end portion; a silica tube housing the said connected ends of the wires and having a closed end immersed in a molten bath and an open end disposed in and cemented to the plug, a graphite sleeve surrounding said wires and having a ared lower open end portion to receive the upper end of the plug in snugtting engagement, a metal tube surrounding said Wires and connected to the sleeve remote from said silica tube, asbestos rope packing covering a portion of said metal tube, and cement covering said sleeve and metal tube, asbestos tape covering a portion of the cement, and Wire covering the tape.

10. An immersion thermocouple for determining the temperature of molten metal comprising a pair of thermoelectrically dissimilar Wires connected together at one end, and a covering for said wires comprising a hollow graphite plug having a tapered upper end portion; a silica tube housing the said connected ends of the wires and having a closed end immersed in a molten bath and an open end disposed in and connected to the plug, a graphite sleeve surrounding said Wires and having a flared lower open end portion to receive the upper end of the plug in snug-fitting engagement, a metal tube surrounding said wires and connected to the sleeve remote from said silica tube, asbestos rope packing covering a portion of said metal tube, and cement covering said sleeve and metal tube, asbestos tape covering a portion of the cement, and Wire dening an elongated open-ended tube engaging and covering the tape.

11. Insulating and protecting means for an immersion thermocouple assembly comprising a tubular metal sleeve to receive a portion of said assembly, refractory materials surrounding said sleeve, and a coil of wire encasing and gripping a portion of said refractory material, said coil of Wire dening an open-ended tube.

12. Insulating and protecting means for an immersion thermocouple assembly comprising a tubular metal sleeve to receive a portion of said assembly, refractory material surrounding said sleeve, and a metal shell gripping and encasing a portion of said refractory material, said metal shell permitting axial thermoexpansion of said refractory material Without substantial relative axial motion between said shell and said refractory material.

LEROY TINGLE. JAM'ES MIDDLETO-N BRANDON.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,019,695 Ross Nov. 5, 1935 2,405,075 Vollrath July 30, 1946 2,476,099 Knudsen July 12, 1949 2,491,823 Maguire Dec. 20, 1949 2,556,238 Tingle June 12, 1951. 

